keep only one typedef for the native drawing context

ui/gfx/native_widget_types.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GFX_NATIVE_WIDGET_TYPES_H_
 #define UI_GFX_NATIVE_WIDGET_TYPES_H_
 
 #include <stdint.h>
 
 #include "base/logging.h"
@@ skipping 119 matching lines @@
 typedef void* NativeCursor;
 typedef ui::ViewAndroid* NativeView;
 typedef ui::WindowAndroid* NativeWindow;
 typedef jobject NativeEvent;
 #else
 #error Unknown build environment.
 #endif
 
 #if defined(OS_WIN)
 typedef HFONT NativeFont;
-typedef HDC NativeDrawingContext;
 typedef IAccessible* NativeViewAccessible;
 #elif defined(OS_IOS)
 typedef UIFont* NativeFont;
-typedef CGContext* NativeDrawingContext;
 #ifdef __OBJC__
 typedef id NativeViewAccessible;
 #else
 typedef void* NativeViewAccessible;
 #endif  // __OBJC__
 #elif defined(OS_MACOSX)
 typedef NSFont* NativeFont;
-typedef CGContext* NativeDrawingContext;
 #ifdef __OBJC__
 typedef id NativeViewAccessible;
 #else
 typedef void* NativeViewAccessible;
 #endif  // __OBJC__
 #else  // Android, Linux, Chrome OS, etc.
 // Linux doesn't have a native font type.
-#if defined(USE_CAIRO)
-typedef cairo_t* NativeDrawingContext;
-#else
-typedef void* NativeDrawingContext;
-#endif  // defined(USE_CAIRO)
 #if defined(USE_X11) && !defined(OS_CHROMEOS)
 typedef AtkObject* NativeViewAccessible;
 #else
 typedef void* NativeViewAccessible;
 #endif
 #endif
 
 // A constant value to indicate that gfx::NativeCursor refers to no cursor.
 #if defined(USE_AURA)
 const int kNullCursor = 0;
@@ skipping 36 matching lines @@
 #elif defined(USE_OZONE)
 typedef int32_t AcceleratedWidget;
 constexpr AcceleratedWidget kNullAcceleratedWidget = 0;
 #else
 #error unknown platform
 #endif
 
 }  // namespace gfx
 
 #endif  // UI_GFX_NATIVE_WIDGET_TYPES_H_